Very few people were treated in hospitals after the accident, indicating that those missing had either escaped or died. "It is a black-and-white situation," said Quebec Health Minister Rejean Hebert, according to Reuters.

The fire's intensity means it is possible that the bodies of some of the victims may never be recovered, Geneviève Guilbault, a spokeswoman for the Quebec coroner’s office, told the Montreal Gazette.

“Right now, we’re working on those we are able to recover,” Guilbault said, according to the newspaper. The five bodies recovered so far will be sent to Montreal for forensic identification.

“We can deduce that many of the bodies are severely burned,” Guilbault said. “That complicates identification, but all necessary means at our disposal will be used to identify them.”

Harper toured the scene on Sunday, calling it an “unbelievable disaster.”

"It looks like a war zone here," he said. "There isn't a family in this area that is not touched by this, that is not affected by this."

Investigators are focusing on how the train’s brakes came to be released.

Firefighters water smoldering rubble in Lac-Megantic, Quebec, on Sunday.Ryan Remiorz / The Canadian Press via AP

"Certainly, the manner in which the train was secured, both hand brakes and air brakes - we'll be looking very strongly at that," Donald Ross of Canada’s Transportation Safety Board told a news conference.

The train’s data recorder has been recovered from the crash site, he added.

Montreal, Maine and Atlantic Railway, the company that owns the train, said in a statement Sunday that a locomotive, left running overnight in order to hold the train in place, had been shut down.

“One fact that has emerged is the locomotive of the oil train parked at Nantes station was shut down subsequent to the departure of the engineer who had handled the train from Farnham, which may have resulted in the release of air brakes on the locomotive that was holding the train in place,” the company said.

Ed Burkhardt, chairman and chief executive of privately owned Rail World, MM&A's parent, told the Wall Street Journal that the engineer had left the hand brakes on all the locomotives and the air brake, a high-pressure stop, on the lead engine.

"He complied with all of the rules," Burkhardt told the newspaper.

Burkhardt said that "several hours" after the engineer left, someone shut down the train—he said he didn't know who it was. "There are some things I would like to know, like who turned off this locomotive," he said.

Sylvain Gilbert, mayor of the town of Nantes – where the train had been parked – told local radio that town firefighters had already dealt with a fire on the train earlier on Friday night, Reuters reported.

It was not clear if that fire was connected in any way to the derailment, or why the train became unsecured in Nantes.

Residents said they were particularly concerned about people who had been inside the Musi-Cafe bar, a popular night spot located next to the center of the blast, Reuters reported.

"There was a big explosion, the heat reached the cafe and then a big wall of fire enveloped the road," said Bernard Theberge, who was sitting on the patio of the restaurant as the train barreled into town. "There were people inside. I thought for maybe two seconds that I should go in, but the heat was too strong to get to the door."

At 7 p.m. on Sunday, more than 40 hours after the accident, firefighters said the blaze was out.

Lac-Megantic, a lakeside town of 6,000 ringed by forests of pine and birch, is in the predominantly French-speaking province of Quebec, about 160 miles east of Montreal and close to the border with Maine and Vermont. About 2,000 people, a third of the population, were evacuated.